1. Field of the Invention
The present invention relates to adhesive tapes, more particularly to tapes that can be firmly adhered to a substrate and can be removed without damaging the substrate.
2. Discussion of the Art
Adhesive tapes, such as, for example, pressure-sensitive adhesive tapes, are usually firmly bonded to substrates because subsequent separation of the tapes from the substrates is neither intended nor desired. However, there are adhesive tapes wherein the adhesives are specifically formulated to allow clean and easy removal from substrates after use, such as, for example, the adhesive used for xe2x80x9cPost-Itxe2x80x9d brand removable notes. These adhesives usually do not exhibit a substantial level of holding power, e.g., greater than 4 to 6 oz./in. adhesion to standard copy paper. Adhesives formulated to provide a substantial level of adhesion, e.g., greater than 30 oz./in. adhesion to paper, are generally difficult to remove without damaging the substrate.
U.S. Pat. No. 4,024,312 discloses a film backed, normally tacky and pressure-sensitive adhesive tape which is highly extensible and highly elastic. The tape can be easily removed from a surface to which it has been applied by stretching it lengthwise in a direction substantially parallel to the plane of the surface. The film backing is formed from a composition comprising elastomeric and thermoplastic A-B-A block copolymers, and possesses a lengthwise elongation to break of at least about 200%, preferably at least about 300%, and a 50% rubber modulus of not above about 2,000 lbs/sq. inch. This low rubber modulus is stated to be an important factor in insuring easy stretchability and easy removal of the tape at high elongations. The elasticity of the backing is important for conformability and other purposes and the elastic recovery from 50% stretch is preferably at least about 75%, more preferably at least about 90%. A preferred use for this tape is the so-called xe2x80x9couchlessxe2x80x9d bandage. German (OS) 3331 016 A1 discloses another adhesive tape for removable adhesive bonds, whereby the tape exhibits high elasticity and low plasticity. The adhesive strength is less than the cohesive strength, and the adhesion capability essentially disappears as the film is being stretched. The ratio of peel force to tear strength of the tape is about 1:2 or greater and the adhesive bond can be released by pulling the film in the direction of the plane of the adhesive joint. The tape is used as a load-resistant adhesive to bond to rigid solid substrates. A separation of the adhesively bonded materials is possible without damage to the substrate.
Both of these tapes are highly elastic and exhibit large recoil when the stretching force is removed, in the same way a rubber band snaps back upon removal of the stretching force. This recoil characteristic can be dangerous, and increases the force required to debond these tapes at low angles. Finally, these highly elastic tapes tend to substantially recover their original shape when the stretching force is removed, and they are therefore not useful for indication of tampering or for guaranteeing single uses for hygienic purposes.
The present invention provides an easily removable, pressure-sensitive adhesive tape comprising a highly extensible, substantially non-recoverable backing, bearing on at least one major surface thereof a layer of pressure-sensitive adhesive, said tape being capable of being firmly bonded to a substrate and being further capable of being removed therefrom after only being stretched at an angle no greater than about 35xc2x0 from the surface of the substrate.
The backing has a Young""s modulus of at least about 2,500 psi, preferably at least about 3,000 psi, but less than about 50,000 psi, more preferably between about 5,000 and about 30,000 psi. The backing preferably has a high tensile strength, a lengthwise elongation at break of at least about 150%, and low recovery, e.g., less than about 50% elastic recovery after being stretched, preferably less than about 30% elastic recovery.
The adhesive layer has sufficient shear strength and adhesive holding power for the specific applications, its adhesive holding power to any substrate preferably being less than its cohesive strength, such that the adhesive layer will not separate from the backing when the backing is subjected to stretching. The adhesive layer is also preferably highly extensible.
The tape can be firmly bonded to a substrate and can then be removed by simply stretching the tape in a direction up to an angle of about 35xc2x0 from the surface of the substrate, preferably up to about 30xc2x0, more preferably up to about 10xc2x0 without leaving traces of adhesive residue on the substrate and without imparting any perceptible damage to the surface of the substrate.
This invention further provides a double coated tape comprising a backing bearing adhesive layers on both major surfaces thereof. The adhesive of each layer can be of equivalent or different chemical composition, of equivalent or different adhesion properties, of equivalent or different thickness, and coated or laminated in the same or different manner.
The tapes of this invention can be used for several purposes. The major uses of the tape of this invention are in the broad categories of mounting and joining. Both of these categories typically involve attachment of two coplanar surfaces by means of the tape, the tape typically bearing adhesive on both major surfaces thereof. Other uses of the tape of this invention are in the categories of labeling and masking. Both of these categories typically involve attachment of the tape to a single surface, the tape typically bearing adhesive on one major surface thereof only.